Bumper crop of new objects revealed beyond Neptune

作者：介埃 发布时间：2019-03-01 06:20:09

By Jeff Hecht Astronomers have found 45 previously unknown bodies of rock and ice orbiting beyond Neptune in the Kuiper Belt. They range from about 50 to 500 kilometres wide. The announcement is probably a record for the most new solar system objects reported simultaneously, increasing the number of distant objects with well defined orbits by nearly 10%. But its real importance will be in measuring the distribution of distant objects well enough to test theories of how the outer solar system evolved. So says Joel Parker at the Southwest Research Institute in Boulder, Colorado, US, a member of the team that found the new objects. About 1100 small objects have been spotted in the outer solar system since the discovery of the first Kuiper Belt Object in 1992. However, astronomers have concentrated more on discovering objects than on tracking them, so about half were never seen again after only brief observation, says Brian Marsden of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics. The Minor Planet Center aids follow-up observers by calculating the preliminary orbits they need to spot the objects again. But when the MPC has only a few days’ worth of data to work with, they have to assume the objects follow common orbits that are circular or, alternatively, linked with Neptune’s orbit. Those assumptions usually work, and the objects are seen again where expected. But they can miss the paths of objects with less-common orbits. “And it’s those few unusual things that really tell you the story of the solar system,” Parker told New Scientist. Different models of how the solar system evolved make different projections of how many objects should occupy certain orbits, so knowing the distribution of objects can support or eliminate some hypotheses. Parker, lead researcher Brett Gladman at the University of British Columbia, Canada, and others were concerned that objects in important orbits might be escaping detection, so in 2003 they launched the Canada France Ecliptic Plane Survey. Initial survey observations were made with the 3.6-metre Canada-France-Hawaii telescope on Mauna Kea. The researchers repeatedly scan regions of the sky where distant objects are most likely to lurk, identify slow-moving candidate objects, then track the objects themselves rather than relying on other groups. Taking this extended data, rather than a brief snapshot, ensured that no mistaken assumptions down the line could cause the objects to evade future detection. “The study was to be as complete and free of ‘recovery bias’ as possible,” Parker explains. In February, after more than two years of accumulating data, they began feeding observations to Marsden at the Minor Planet Center. The 45 new objects yielded by observations are described in the Minor Planet Electronic Circular issued on Saturday. Meanwhile, Gladman’s group is now analysing the differences between the orbital distributions recorded by its survey and in previous,